//! Multi-API chat client: Ollama (default), OpenAI, Anthropic.
//!
//! The wire format is selected via the optional `api` input:
//!
//! - `ollama` (default) — Ollama `/api/chat`; unchanged v0.1.0
//!   behavior including the best-effort model-digest probe.
//! - `openai` — OpenAI Chat Completions wire format
//!   (`/v1/chat/completions`), the de-facto standard implemented
//!   by vLLM and most self-hosted inference servers. Bearer auth.
//! - `anthropic` — Anthropic Messages API (`/v1/messages`),
//!   `x-api-key` + `anthropic-version` headers, top-level
//!   `system` field, mandatory `max_tokens`.
//!
//! No streaming, no tool calls — one prompt in, one completion out.
//!
//! All HTTP I/O lives behind a `LlmClient` trait so unit tests can
//! exercise request building, response parsing, and the digest
//! probe on the host without making real network calls.

use serde::Serialize;

/// Anthropic's Messages API requires `max_tokens`. This default is
/// large enough for document-processing completions while staying
/// well below every current model's output cap.
const ANTHROPIC_DEFAULT_MAX_TOKENS: u32 = 4096;

/// Pinned Messages API version header. Anthropic keeps old
/// versions working; bump deliberately, never implicitly.
const ANTHROPIC_VERSION: &str = "2023-06-01";

#[allow(dead_code)]
#[derive(Debug, thiserror::Error)]
pub enum LlmError {
    #[error("missing required input '{0}'")]
    MissingInput(&'static str),
    #[error("unsupported api '{0}' (expected: ollama, openai, anthropic)")]
    UnsupportedApi(String),
    #[error("http error: {0}")]
    Http(String),
    #[error("non-success status: {0}")]
    Status(u16),
    #[error("response body could not be parsed as the expected schema: {0}")]
    Decode(String),
}

/// Which wire format to speak. Selected by the `api` input.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Api {
    Ollama,
    Openai,
    Anthropic,
}

impl Api {
    /// Parse the `api` input. Empty string means the input was not
    /// provided and falls back to Ollama (v0.1.0 behavior).
    pub fn parse(raw: &str) -> Result<Self, LlmError> {
        match raw.trim().to_ascii_lowercase().as_str() {
            "" | "ollama" => Ok(Api::Ollama),
            "openai" => Ok(Api::Openai),
            "anthropic" => Ok(Api::Anthropic),
            other => Err(LlmError::UnsupportedApi(other.to_string())),
        }
    }
}

pub trait LlmClient {
    /// POST `body` as JSON to `url` with the given extra headers.
    /// `Content-Type: application/json` is implied. Header VALUES
    /// may carry credentials — implementations must never log them.
    fn post_json(
        &self,
        url: &str,
        body: &str,
        headers: &[(&'static str, String)],
    ) -> Result<String, LlmError>;
}

#[derive(Debug, Clone)]
pub struct ChatParams<'a> {
    pub api: Api,
    pub endpoint: &'a str,
    pub model: &'a str,
    pub api_key: &'a str,
    pub system_prompt: &'a str,
    pub prompt: &'a str,
}

/// Auth/protocol headers for the selected API. The api_key is only
/// ever placed into a header value here; it must not appear in any
/// error, output, or log line.
pub fn build_headers(p: &ChatParams) -> Vec<(&'static str, String)> {
    let mut headers = Vec::with_capacity(2);
    match p.api {
        Api::Ollama | Api::Openai => {
            if !p.api_key.is_empty() {
                headers.push(("Authorization", format!("Bearer {}", p.api_key)));
            }
        }
        Api::Anthropic => {
            if !p.api_key.is_empty() {
                headers.push(("x-api-key", p.api_key.to_string()));
            }
            headers.push(("anthropic-version", ANTHROPIC_VERSION.to_string()));
        }
    }
    headers
}

#[derive(Serialize)]
struct ChatMessage<'a> {
    role: &'a str,
    content: &'a str,
}

#[derive(Serialize)]
struct OllamaRequest<'a> {
    model: &'a str,
    messages: Vec<ChatMessage<'a>>,
    stream: bool,
}

#[derive(Serialize)]
struct OpenAiRequest<'a> {
    model: &'a str,
    messages: Vec<ChatMessage<'a>>,
    stream: bool,
}

#[derive(Serialize)]
struct AnthropicRequest<'a> {
    model: &'a str,
    max_tokens: u32,
    #[serde(skip_serializing_if = "Option::is_none")]
    system: Option<&'a str>,
    messages: Vec<ChatMessage<'a>>,
}

/// System-then-user message list shared by the Ollama and OpenAI
/// wire formats. The system message is omitted when empty so a
/// deployment can use the model's built-in system prompt.
fn build_messages<'a>(p: &ChatParams<'a>) -> Vec<ChatMessage<'a>> {
    let mut messages = Vec::with_capacity(2);
    if !p.system_prompt.is_empty() {
        messages.push(ChatMessage {
            role: "system",
            content: p.system_prompt,
        });
    }
    messages.push(ChatMessage {
        role: "user",
        content: p.prompt,
    });
    messages
}

/// Build the request body for an Ollama `/api/chat` invocation.
pub fn build_ollama_body(p: &ChatParams) -> String {
    let req = OllamaRequest {
        model: p.model,
        messages: build_messages(p),
        stream: false,
    };
    serde_json::to_string(&req).unwrap_or_else(|_| String::from("{}"))
}

/// Build the request body for an OpenAI-compatible
/// `/v1/chat/completions` invocation (OpenAI, vLLM, most
/// self-hosted inference servers).
pub fn build_openai_body(p: &ChatParams) -> String {
    let req = OpenAiRequest {
        model: p.model,
        messages: build_messages(p),
        stream: false,
    };
    serde_json::to_string(&req).unwrap_or_else(|_| String::from("{}"))
}

/// Build the request body for an Anthropic `/v1/messages`
/// invocation. `system` is a top-level field (not a message);
/// `max_tokens` is mandatory in the Messages API.
pub fn build_anthropic_body(p: &ChatParams) -> String {
    let req = AnthropicRequest {
        model: p.model,
        max_tokens: ANTHROPIC_DEFAULT_MAX_TOKENS,
        system: if p.system_prompt.is_empty() {
            None
        } else {
            Some(p.system_prompt)
        },
        messages: vec![ChatMessage {
            role: "user",
            content: p.prompt,
        }],
    };
    serde_json::to_string(&req).unwrap_or_else(|_| String::from("{}"))
}

/// Extract the assistant's message text from an Ollama
/// /api/chat response.
pub fn extract_ollama_content(body: &str) -> Result<String, LlmError> {
    let v: serde_json::Value =
        serde_json::from_str(body).map_err(|e| LlmError::Decode(e.to_string()))?;
    v.get("message")
        .and_then(|m| m.get("content"))
        .and_then(|c| c.as_str())
        .map(|s| s.to_string())
        .ok_or_else(|| LlmError::Decode("missing message.content".into()))
}

/// Extract the assistant text from an OpenAI Chat Completions
/// response: `choices[0].message.content`.
pub fn extract_openai_content(body: &str) -> Result<String, LlmError> {
    let v: serde_json::Value =
        serde_json::from_str(body).map_err(|e| LlmError::Decode(e.to_string()))?;
    v.get("choices")
        .and_then(|c| c.get(0))
        .and_then(|c| c.get("message"))
        .and_then(|m| m.get("content"))
        .and_then(|c| c.as_str())
        .map(|s| s.to_string())
        .ok_or_else(|| LlmError::Decode("missing choices[0].message.content".into()))
}

/// Extract the assistant text from an Anthropic Messages
/// response: `content[0].text`.
pub fn extract_anthropic_content(body: &str) -> Result<String, LlmError> {
    let v: serde_json::Value =
        serde_json::from_str(body).map_err(|e| LlmError::Decode(e.to_string()))?;
    v.get("content")
        .and_then(|c| c.get(0))
        .and_then(|c| c.get("text"))
        .and_then(|t| t.as_str())
        .map(|s| s.to_string())
        .ok_or_else(|| LlmError::Decode("missing content[0].text".into()))
}

#[derive(Debug, Clone)]
pub struct ChatWithIdentity {
    pub response: String,
    pub model_digest: Option<String>,
}

/// Run one chat call in the selected wire format AND, for Ollama,
/// probe the model digest. The probe is best-effort — non-Ollama
/// APIs expose no digest endpoint, so `model_digest = None` there
/// (documented empty, never invented); transient probe failures on
/// Ollama also yield `None` rather than failing the whole call.
pub fn chat_with_identity<C: LlmClient>(
    client: &C,
    p: &ChatParams,
) -> Result<ChatWithIdentity, LlmError> {
    if p.endpoint.is_empty() {
        return Err(LlmError::MissingInput("endpoint"));
    }
    if p.model.is_empty() {
        return Err(LlmError::MissingInput("model"));
    }
    if p.prompt.is_empty() {
        return Err(LlmError::MissingInput("prompt"));
    }
    let body = match p.api {
        Api::Ollama => build_ollama_body(p),
        Api::Openai => build_openai_body(p),
        Api::Anthropic => build_anthropic_body(p),
    };
    let headers = build_headers(p);
    let response_body = client.post_json(p.endpoint, &body, &headers)?;
    let response = match p.api {
        Api::Ollama => extract_ollama_content(&response_body)?,
        Api::Openai => extract_openai_content(&response_body)?,
        Api::Anthropic => extract_anthropic_content(&response_body)?,
    };
    let model_digest = match p.api {
        Api::Ollama => probe_model_digest(client, p),
        Api::Openai | Api::Anthropic => None,
    };
    Ok(ChatWithIdentity {
        response,
        model_digest,
    })
}

fn probe_model_digest<C: LlmClient>(client: &C, p: &ChatParams) -> Option<String> {
    let show_url = derive_show_url(p.endpoint)?;
    let body = serde_json::to_string(&serde_json::json!({ "name": p.model })).ok()?;
    let headers = build_headers(p);
    let response = client.post_json(&show_url, &body, &headers).ok()?;
    extract_show_digest(&response)
}

pub fn derive_show_url(chat_endpoint: &str) -> Option<String> {
    if chat_endpoint.ends_with("/api/chat") {
        let head_len = chat_endpoint.len() - "/api/chat".len();
        let mut url = String::with_capacity(head_len + "/api/show".len());
        url.push_str(&chat_endpoint[..head_len]);
        url.push_str("/api/show");
        Some(url)
    } else {
        None
    }
}

pub fn extract_show_digest(body: &str) -> Option<String> {
    let v: serde_json::Value = serde_json::from_str(body).ok()?;
    let candidates = [
        v.get("digest"),
        v.get("details").and_then(|d| d.get("digest")),
        v.get("model_info").and_then(|d| d.get("digest")),
    ];
    for cand in candidates {
        if let Some(s) = cand.and_then(|v| v.as_str()) {
            if !s.is_empty() {
                return Some(s.to_string());
            }
        }
    }
    None
}

#[cfg(test)]
mod tests {
    #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
    use super::*;
    use std::cell::RefCell;

    /// (url, body, headers) of one recorded call.
    type RecordedCall = (String, String, Vec<(String, String)>);

    struct MockClient {
        responses: RefCell<Vec<Result<String, LlmError>>>,
        /// Every call, in call order.
        calls: RefCell<Vec<RecordedCall>>,
    }

    impl MockClient {
        fn new(responses: Vec<Result<String, LlmError>>) -> Self {
            Self {
                responses: RefCell::new(responses),
                calls: RefCell::new(Vec::new()),
            }
        }
    }

    impl LlmClient for MockClient {
        fn post_json(
            &self,
            url: &str,
            body: &str,
            headers: &[(&'static str, String)],
        ) -> Result<String, LlmError> {
            self.calls.borrow_mut().push((
                url.to_string(),
                body.to_string(),
                headers
                    .iter()
                    .map(|(k, v)| (k.to_string(), v.clone()))
                    .collect(),
            ));
            self.responses
                .borrow_mut()
                .pop()
                .unwrap_or(Err(LlmError::Http("no more mock responses".into())))
        }
    }

    fn params<'a>(api: Api) -> ChatParams<'a> {
        ChatParams {
            api,
            endpoint: "http://x/api/chat",
            model: "qwen",
            api_key: "",
            system_prompt: "",
            prompt: "hello",
        }
    }

    // ---------------- api input parsing ----------------

    #[test]
    fn api_parse_defaults_to_ollama() {
        assert_eq!(Api::parse("").unwrap(), Api::Ollama);
        assert_eq!(Api::parse("ollama").unwrap(), Api::Ollama);
        assert_eq!(Api::parse("  OpenAI ").unwrap(), Api::Openai);
        assert_eq!(Api::parse("anthropic").unwrap(), Api::Anthropic);
    }

    #[test]
    fn api_parse_rejects_unknown() {
        assert!(matches!(
            Api::parse("gemini"),
            Err(LlmError::UnsupportedApi(_))
        ));
    }

    // ---------------- Ollama wire format (regression) ----------------

    #[test]
    fn ollama_body_includes_system_when_provided() {
        let p = ChatParams {
            system_prompt: "be helpful",
            ..params(Api::Ollama)
        };
        let body = build_ollama_body(&p);
        let v: serde_json::Value = serde_json::from_str(&body).unwrap();
        let messages = v["messages"].as_array().unwrap();
        assert_eq!(messages.len(), 2);
        assert_eq!(messages[0]["role"], "system");
        assert_eq!(messages[0]["content"], "be helpful");
        assert_eq!(messages[1]["role"], "user");
        assert_eq!(messages[1]["content"], "hello");
        assert_eq!(v["stream"], false);
    }

    #[test]
    fn ollama_body_omits_system_when_empty() {
        let body = build_ollama_body(&params(Api::Ollama));
        let v: serde_json::Value = serde_json::from_str(&body).unwrap();
        let messages = v["messages"].as_array().unwrap();
        assert_eq!(messages.len(), 1);
        assert_eq!(messages[0]["role"], "user");
    }

    #[test]
    fn extract_content_pulls_message_content() {
        let body = r#"{"message":{"role":"assistant","content":"hi there"},"done":true}"#;
        assert_eq!(extract_ollama_content(body).unwrap(), "hi there");
    }

    #[test]
    fn extract_content_errors_on_missing_field() {
        let body = r#"{"done":true}"#;
        assert!(matches!(
            extract_ollama_content(body),
            Err(LlmError::Decode(_))
        ));
    }

    #[test]
    fn ollama_bearer_header_only_with_key() {
        assert!(build_headers(&params(Api::Ollama)).is_empty());
        let p = ChatParams {
            api_key: "sk-test",
            ..params(Api::Ollama)
        };
        assert_eq!(
            build_headers(&p),
            vec![("Authorization", "Bearer sk-test".to_string())]
        );
    }

    // ---------------- OpenAI wire format ----------------

    #[test]
    fn openai_body_matches_chat_completions_format() {
        let p = ChatParams {
            api: Api::Openai,
            endpoint: "http://vllm:8000/v1/chat/completions",
            model: "meta-llama/Llama-3.1-8B-Instruct",
            api_key: "sk-x",
            system_prompt: "be terse",
            prompt: "hello",
        };
        let body = build_openai_body(&p);
        let v: serde_json::Value = serde_json::from_str(&body).unwrap();
        assert_eq!(v["model"], "meta-llama/Llama-3.1-8B-Instruct");
        assert_eq!(v["stream"], false);
        let messages = v["messages"].as_array().unwrap();
        assert_eq!(messages.len(), 2);
        assert_eq!(messages[0]["role"], "system");
        assert_eq!(messages[0]["content"], "be terse");
        assert_eq!(messages[1]["role"], "user");
        assert_eq!(messages[1]["content"], "hello");
        // No Anthropic-only fields leak into the OpenAI body.
        assert!(v.get("max_tokens").is_none());
        assert!(v.get("system").is_none());
    }

    #[test]
    fn openai_response_parses_fixture() {
        // Shape as returned by OpenAI / vLLM /v1/chat/completions.
        let body = r#"{
            "id": "chatcmpl-123",
            "object": "chat.completion",
            "created": 1719000000,
            "model": "meta-llama/Llama-3.1-8B-Instruct",
            "choices": [{
                "index": 0,
                "message": {"role": "assistant", "content": "Hi from vLLM"},
                "finish_reason": "stop"
            }],
            "usage": {"prompt_tokens": 9, "completion_tokens": 4, "total_tokens": 13}
        }"#;
        assert_eq!(extract_openai_content(body).unwrap(), "Hi from vLLM");
    }

    #[test]
    fn openai_response_errors_on_missing_choices() {
        assert!(matches!(
            extract_openai_content(r#"{"object":"chat.completion","choices":[]}"#),
            Err(LlmError::Decode(_))
        ));
        assert!(matches!(
            extract_openai_content(r#"{"error":{"message":"invalid key"}}"#),
            Err(LlmError::Decode(_))
        ));
    }

    #[test]
    fn openai_uses_bearer_auth() {
        let p = ChatParams {
            api_key: "sk-test",
            ..params(Api::Openai)
        };
        assert_eq!(
            build_headers(&p),
            vec![("Authorization", "Bearer sk-test".to_string())]
        );
    }

    #[test]
    fn openai_chat_returns_content_and_no_digest() {
        let canned = r#"{"choices":[{"message":{"role":"assistant","content":"ok"}}]}"#;
        let client = MockClient::new(vec![Ok(canned.to_string())]);
        let p = ChatParams {
            api: Api::Openai,
            endpoint: "http://vllm:8000/v1/chat/completions",
            model: "m",
            api_key: "sk",
            system_prompt: "",
            prompt: "hi",
        };
        let result = chat_with_identity(&client, &p).unwrap();
        assert_eq!(result.response, "ok");
        // No digest API on OpenAI-compatible endpoints — documented
        // empty, and exactly one HTTP call (no probe).
        assert_eq!(result.model_digest, None);
        assert_eq!(client.calls.borrow().len(), 1);
    }

    // ---------------- Anthropic wire format ----------------

    #[test]
    fn anthropic_body_matches_messages_format() {
        let p = ChatParams {
            api: Api::Anthropic,
            endpoint: "https://api.anthropic.com/v1/messages",
            model: "claude-fable-5",
            api_key: "sk-ant",
            system_prompt: "be terse",
            prompt: "hello",
        };
        let body = build_anthropic_body(&p);
        let v: serde_json::Value = serde_json::from_str(&body).unwrap();
        assert_eq!(v["model"], "claude-fable-5");
        // max_tokens is mandatory in the Messages API.
        assert_eq!(v["max_tokens"], 4096);
        // system is a top-level field, never a message.
        assert_eq!(v["system"], "be terse");
        let messages = v["messages"].as_array().unwrap();
        assert_eq!(messages.len(), 1);
        assert_eq!(messages[0]["role"], "user");
        assert_eq!(messages[0]["content"], "hello");
        // No OpenAI/Ollama-only fields leak in.
        assert!(v.get("stream").is_none());
    }

    #[test]
    fn anthropic_body_omits_system_when_empty() {
        let body = build_anthropic_body(&params(Api::Anthropic));
        let v: serde_json::Value = serde_json::from_str(&body).unwrap();
        assert!(v.get("system").is_none());
        assert_eq!(v["max_tokens"], 4096);
    }

    #[test]
    fn anthropic_response_parses_fixture() {
        // Shape as returned by the Anthropic Messages API.
        let body = r#"{
            "id": "msg_01XFDUDYJgAACzvnptvVoYEL",
            "type": "message",
            "role": "assistant",
            "model": "claude-fable-5",
            "content": [{"type": "text", "text": "Hi from Claude"}],
            "stop_reason": "end_turn",
            "usage": {"input_tokens": 10, "output_tokens": 5}
        }"#;
        assert_eq!(extract_anthropic_content(body).unwrap(), "Hi from Claude");
    }

    #[test]
    fn anthropic_response_errors_on_missing_content() {
        assert!(matches!(
            extract_anthropic_content(r#"{"type":"message","content":[]}"#),
            Err(LlmError::Decode(_))
        ));
        assert!(matches!(
            extract_anthropic_content(r#"{"type":"error","error":{"message":"x"}}"#),
            Err(LlmError::Decode(_))
        ));
    }

    #[test]
    fn anthropic_uses_x_api_key_and_version_headers() {
        let p = ChatParams {
            api_key: "sk-ant-test",
            ..params(Api::Anthropic)
        };
        let headers = build_headers(&p);
        assert_eq!(
            headers,
            vec![
                ("x-api-key", "sk-ant-test".to_string()),
                ("anthropic-version", "2023-06-01".to_string()),
            ]
        );
        // Never Bearer auth on the Anthropic path.
        assert!(headers.iter().all(|(k, _)| *k != "Authorization"));
    }

    #[test]
    fn anthropic_chat_returns_content_and_no_digest() {
        let canned = r#"{"content":[{"type":"text","text":"ok"}]}"#;
        let client = MockClient::new(vec![Ok(canned.to_string())]);
        let p = ChatParams {
            api: Api::Anthropic,
            endpoint: "https://api.anthropic.com/v1/messages",
            model: "claude-fable-5",
            api_key: "sk-ant",
            system_prompt: "",
            prompt: "hi",
        };
        let result = chat_with_identity(&client, &p).unwrap();
        assert_eq!(result.response, "ok");
        assert_eq!(result.model_digest, None);
        assert_eq!(client.calls.borrow().len(), 1);
    }

    // ---------------- digest probe (Ollama only) ----------------

    #[test]
    fn derive_show_url_swaps_chat_suffix() {
        assert_eq!(
            derive_show_url("http://localhost:11434/api/chat").as_deref(),
            Some("http://localhost:11434/api/show")
        );
    }

    #[test]
    fn derive_show_url_returns_none_for_non_ollama() {
        assert!(derive_show_url("https://api.openai.com/v1/chat/completions").is_none());
    }

    #[test]
    fn extract_show_digest_finds_top_level() {
        let body = r#"{"digest":"sha256:abc"}"#;
        assert_eq!(extract_show_digest(body).as_deref(), Some("sha256:abc"));
    }

    #[test]
    fn extract_show_digest_falls_back_to_nested() {
        let body = r#"{"details":{"digest":"sha256:nested"}}"#;
        assert_eq!(extract_show_digest(body).as_deref(), Some("sha256:nested"));
    }

    #[test]
    fn chat_with_identity_records_digest_when_show_responds() {
        let canned_chat = r#"{"message":{"content":"the response"},"done":true}"#.to_string();
        let canned_show = r#"{"digest":"sha256:deadbeef"}"#.to_string();
        let client = MockClient::new(vec![Ok(canned_show), Ok(canned_chat)]);
        let p = ChatParams {
            endpoint: "http://localhost:11434/api/chat",
            ..params(Api::Ollama)
        };
        let result = chat_with_identity(&client, &p).unwrap();
        assert_eq!(result.response, "the response");
        assert_eq!(result.model_digest.as_deref(), Some("sha256:deadbeef"));
    }

    #[test]
    fn chat_with_identity_swallows_show_failure() {
        let canned_chat = r#"{"message":{"content":"ok"}}"#.to_string();
        let client = MockClient::new(vec![Err(LlmError::Status(500)), Ok(canned_chat)]);
        let p = ChatParams {
            endpoint: "http://localhost:11434/api/chat",
            ..params(Api::Ollama)
        };
        let result = chat_with_identity(&client, &p).unwrap();
        assert_eq!(result.response, "ok");
        assert_eq!(result.model_digest, None);
    }

    #[test]
    fn chat_with_identity_skips_probe_for_non_ollama_url() {
        let canned_chat = r#"{"message":{"content":"ok"}}"#.to_string();
        let client = MockClient::new(vec![Ok(canned_chat)]);
        let p = ChatParams {
            endpoint: "https://example.com/proxy/chat",
            ..params(Api::Ollama)
        };
        let result = chat_with_identity(&client, &p).unwrap();
        assert_eq!(result.response, "ok");
        assert_eq!(result.model_digest, None);
    }

    // ---------------- input guards ----------------

    #[test]
    fn empty_prompt_is_rejected() {
        let client = MockClient::new(vec![]);
        let p = ChatParams {
            prompt: "",
            ..params(Api::Ollama)
        };
        assert!(matches!(
            chat_with_identity(&client, &p),
            Err(LlmError::MissingInput("prompt"))
        ));
    }
}