package ollama

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"net/http"
	"strings"
)

// scannerBufSize is the buffer size for the NDJSON scanner (4 MB).
// Large enough to handle big tool-call payloads in a single line.
const scannerBufSize = 4 * 1024 * 1024

// Client defines the interface for communicating with an Ollama target.
//
// Why: an interface allows the worker loop, passthrough handlers, and tests to
// share a single contract and swap in stubs.
// What: covers the four Ollama endpoints foreman uses: chat, embed, tags, and ps.
// Test: implement with a stub HTTP server; verify round-trip for each method.
type Client interface {
	// Chat sends a chat request. When stream is false, returns (*ChatResponse, nil, nil).
	// When stream is true, returns (nil, <-chan ChatResponse, nil) with chunks delivered
	// on the channel. The channel is closed when the stream ends.
	Chat(ctx context.Context, req ChatRequest, stream bool) (*ChatResponse, <-chan ChatResponse, error)

	// Embed sends an embedding request to /api/embed.
	Embed(ctx context.Context, req EmbedRequest) (*EmbedResponse, error)

	// Tags returns the list of installed models from /api/tags.
	Tags(ctx context.Context) (*TagsResponse, error)

	// Ps returns the list of currently-loaded models from /api/ps.
	Ps(ctx context.Context) (*PsResponse, error)

	// RawChat performs a raw proxied chat request, returning the http.Response for
	// the caller to stream directly to a downstream client. The caller is responsible
	// for closing the response body.
	RawChat(ctx context.Context, body []byte) (*http.Response, error)

	// RawEmbed performs a raw proxied embed request, returning the http.Response.
	// The caller is responsible for closing the response body.
	RawEmbed(ctx context.Context, body []byte) (*http.Response, error)
}

// httpClient is the concrete implementation of Client backed by net/http.
type httpClient struct {
	baseURL    string
	token      string
	httpClient *http.Client
}

// NewClient creates a new Ollama HTTP client.
//
// Why: centralizes base URL, auth token, and HTTP client configuration.
// What: returns a Client that makes HTTP requests to the given Ollama base URL.
// Test: create with a httptest.Server URL, call Tags, verify correct request path.
func NewClient(baseURL, token string) Client {
	// Trim trailing slash for consistent URL construction.
	baseURL = strings.TrimRight(baseURL, "/")
	return &httpClient{
		baseURL:    baseURL,
		token:      token,
		httpClient: &http.Client{},
	}
}

// Chat sends a POST /api/chat to the Ollama target.
//
// Why: the worker loop and sync passthrough both need structured chat access.
// What: POSTs the chat request, returns either a single response or a channel of
// streamed chunks depending on the stream parameter.
// Test: stub a /api/chat endpoint returning NDJSON or a single JSON object; verify
// both streaming and non-streaming paths.
func (c *httpClient) Chat(ctx context.Context, req ChatRequest, stream bool) (*ChatResponse, <-chan ChatResponse, error) {
	streamVal := stream
	req.Stream = &streamVal

	body, err := json.Marshal(req)
	if err != nil {
		return nil, nil, fmt.Errorf("marshal chat request: %w", err)
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/api/chat", bytes.NewReader(body))
	if err != nil {
		return nil, nil, fmt.Errorf("create chat request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")
	c.setAuth(httpReq)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, nil, c.wrapConnErr(err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		defer resp.Body.Close()
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, nil, &HTTPError{StatusCode: resp.StatusCode, Body: string(errBody)}
	}

	if !stream {
		defer resp.Body.Close()
		var chatResp ChatResponse
		if err := json.NewDecoder(resp.Body).Decode(&chatResp); err != nil {
			return nil, nil, fmt.Errorf("decode chat response: %w", err)
		}
		return &chatResp, nil, nil
	}

	// Streaming: read NDJSON lines and send on channel.
	ch := make(chan ChatResponse, 64)
	go func() {
		defer close(ch)
		defer resp.Body.Close()

		scanner := bufio.NewScanner(resp.Body)
		scanner.Buffer(make([]byte, 0, scannerBufSize), scannerBufSize)
		for scanner.Scan() {
			line := scanner.Bytes()
			if len(line) == 0 {
				continue
			}
			var chunk ChatResponse
			if err := json.Unmarshal(line, &chunk); err != nil {
				continue
			}
			ch <- chunk
		}
	}()

	return nil, ch, nil
}

// Embed sends a POST /api/embed to the Ollama target.
//
// Why: embedding requests bypass the queue and go directly to the target (ADR-0013).
// What: POSTs the embed request and returns the parsed response.
// Test: stub /api/embed, send a request, verify embeddings in the response.
func (c *httpClient) Embed(ctx context.Context, req EmbedRequest) (*EmbedResponse, error) {
	body, err := json.Marshal(req)
	if err != nil {
		return nil, fmt.Errorf("marshal embed request: %w", err)
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/api/embed", bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("create embed request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")
	c.setAuth(httpReq)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, c.wrapConnErr(err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, &HTTPError{StatusCode: resp.StatusCode, Body: string(errBody)}
	}

	var embedResp EmbedResponse
	if err := json.NewDecoder(resp.Body).Decode(&embedResp); err != nil {
		return nil, fmt.Errorf("decode embed response: %w", err)
	}
	return &embedResp, nil
}

// Tags fetches GET /api/tags from the Ollama target.
//
// Why: the model poller needs the installed model list for inventory and validation.
// What: GETs /api/tags and returns the parsed response.
// Test: stub /api/tags with a model list, verify Tags() returns it.
func (c *httpClient) Tags(ctx context.Context) (*TagsResponse, error) {
	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+"/api/tags", nil)
	if err != nil {
		return nil, fmt.Errorf("create tags request: %w", err)
	}
	c.setAuth(httpReq)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, c.wrapConnErr(err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, &HTTPError{StatusCode: resp.StatusCode, Body: string(errBody)}
	}

	var tagsResp TagsResponse
	if err := json.NewDecoder(resp.Body).Decode(&tagsResp); err != nil {
		return nil, fmt.Errorf("decode tags response: %w", err)
	}
	return &tagsResp, nil
}

// Ps fetches GET /api/ps from the Ollama target.
//
// Why: the poller and scheduler need to know which models are currently loaded.
// What: GETs /api/ps and returns the parsed response.
// Test: stub /api/ps with running models, verify Ps() returns them.
func (c *httpClient) Ps(ctx context.Context) (*PsResponse, error) {
	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+"/api/ps", nil)
	if err != nil {
		return nil, fmt.Errorf("create ps request: %w", err)
	}
	c.setAuth(httpReq)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, c.wrapConnErr(err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, &HTTPError{StatusCode: resp.StatusCode, Body: string(errBody)}
	}

	var psResp PsResponse
	if err := json.NewDecoder(resp.Body).Decode(&psResp); err != nil {
		return nil, fmt.Errorf("decode ps response: %w", err)
	}
	return &psResp, nil
}

// RawChat performs a raw proxied POST /api/chat, returning the http.Response for
// direct streaming to a downstream client.
//
// Why: the passthrough handler needs raw access to the response body for NDJSON
// streaming without double-parsing.
// What: POSTs the raw body to /api/chat and returns the raw HTTP response.
// Test: stub /api/chat, call RawChat, verify response status and body forwarding.
func (c *httpClient) RawChat(ctx context.Context, body []byte) (*http.Response, error) {
	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/api/chat", bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("create raw chat request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")
	c.setAuth(httpReq)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, c.wrapConnErr(err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		defer resp.Body.Close()
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, &HTTPError{StatusCode: resp.StatusCode, Body: string(errBody)}
	}

	return resp, nil
}

// RawEmbed performs a raw proxied POST /api/embed, returning the http.Response.
//
// Why: the embed passthrough handler proxies the raw body/response without parsing.
// What: POSTs the raw body to /api/embed and returns the raw HTTP response.
// Test: stub /api/embed, call RawEmbed, verify response forwarding.
func (c *httpClient) RawEmbed(ctx context.Context, body []byte) (*http.Response, error) {
	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/api/embed", bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("create raw embed request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")
	c.setAuth(httpReq)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, c.wrapConnErr(err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		defer resp.Body.Close()
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, &HTTPError{StatusCode: resp.StatusCode, Body: string(errBody)}
	}

	return resp, nil
}

// setAuth adds the bearer token to the request if configured.
func (c *httpClient) setAuth(req *http.Request) {
	if c.token != "" {
		req.Header.Set("Authorization", "Bearer "+c.token)
	}
}

// wrapConnErr checks if the error is a network-level failure and wraps it in a
// ConnectionError. Non-network errors are returned as-is.
func (c *httpClient) wrapConnErr(err error) error {
	if err == nil {
		return nil
	}
	// Check for common network error types.
	if _, ok := err.(*net.OpError); ok {
		return &ConnectionError{URL: c.baseURL, Err: err}
	}
	if _, ok := err.(net.Error); ok {
		return &ConnectionError{URL: c.baseURL, Err: err}
	}
	// Also catch connection refused, DNS errors, etc. that might be wrapped.
	if isConnectionError(err) {
		return &ConnectionError{URL: c.baseURL, Err: err}
	}
	return err
}

// isConnectionError checks for common connection-level error patterns in wrapped errors.
func isConnectionError(err error) bool {
	msg := err.Error()
	return strings.Contains(msg, "connection refused") ||
		strings.Contains(msg, "no such host") ||
		strings.Contains(msg, "network is unreachable") ||
		strings.Contains(msg, "i/o timeout") ||
		strings.Contains(msg, "dial tcp")
}