// ollama.go — Provider backed by an Ollama HTTP server. Compatible
// with Ollama 0.21+ via the per-text /api/embeddings endpoint.
// Newer Ollama (0.4+) exposes /api/embed for batched calls, but
// the per-text loop is forward-compatible with both.
package embed

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

// OllamaProvider hits an Ollama server at the configured base URL.
type OllamaProvider struct {
	baseURL      string
	defaultModel string
	hc           *http.Client
}

// NewOllama builds a provider against baseURL (e.g.
// "http://localhost:11434"). defaultModel is what gets used when
// callers pass an empty model name.
func NewOllama(baseURL, defaultModel string) *OllamaProvider {
	return &OllamaProvider{
		baseURL:      strings.TrimRight(baseURL, "/"),
		defaultModel: defaultModel,
		hc: &http.Client{
			// Embeddings are CPU-bound on the server side; 60s gives
			// plenty of headroom for a single-text call. Caller can
			// add an outer ctx deadline for batch-level cap.
			Timeout: 60 * time.Second,
		},
	}
}

// ollamaRequest is Ollama's /api/embeddings body shape.
type ollamaRequest struct {
	Model  string `json:"model"`
	Prompt string `json:"prompt"`
}

// ollamaResponse mirrors the success body. Embedding is float64
// from Ollama; we convert to float32 at the boundary.
type ollamaResponse struct {
	Embedding []float64 `json:"embedding"`
}

// Embed loops over texts, issuing one HTTP call per text. Errors
// short-circuit — if call N fails, we return the error and the
// caller sees no partial Result.
func (p *OllamaProvider) Embed(ctx context.Context, texts []string, model string) (Result, error) {
	if len(texts) == 0 {
		return Result{}, ErrEmptyTexts
	}
	if model == "" {
		model = p.defaultModel
	}
	if model == "" {
		return Result{}, fmt.Errorf("embed: no model (empty request, no default)")
	}

	out := Result{Model: model, Vectors: make([][]float32, 0, len(texts))}
	for i, text := range texts {
		vec, err := p.embedOne(ctx, model, text)
		if err != nil {
			return Result{}, fmt.Errorf("embed text[%d]: %w", i, err)
		}
		// Per-text vectors must agree on dimension. Lock on first.
		if out.Dimension == 0 {
			out.Dimension = len(vec)
		} else if len(vec) != out.Dimension {
			return Result{}, fmt.Errorf("%w: text[%d] returned %d, prior were %d",
				ErrModelMismatch, i, len(vec), out.Dimension)
		}
		out.Vectors = append(out.Vectors, vec)
	}
	return out, nil
}

func (p *OllamaProvider) embedOne(ctx context.Context, model, text string) ([]float32, error) {
	body, err := json.Marshal(ollamaRequest{Model: model, Prompt: text})
	if err != nil {
		return nil, fmt.Errorf("marshal: %w", err)
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
		p.baseURL+"/api/embeddings", bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("req: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.ContentLength = int64(len(body))

	resp, err := p.hc.Do(req)
	if err != nil {
		return nil, fmt.Errorf("do: %w", err)
	}
	defer drainAndClose(resp.Body)

	if resp.StatusCode != http.StatusOK {
		preview, _ := io.ReadAll(io.LimitReader(resp.Body, 256))
		return nil, fmt.Errorf("upstream status %d: %s", resp.StatusCode, string(preview))
	}
	var or ollamaResponse
	if err := json.NewDecoder(resp.Body).Decode(&or); err != nil {
		return nil, fmt.Errorf("decode: %w", err)
	}
	if len(or.Embedding) == 0 {
		return nil, fmt.Errorf("upstream returned empty embedding")
	}
	// Float64 → Float32. Loss of precision is acceptable for HNSW
	// search; float32 matches the rest of the system.
	out := make([]float32, len(or.Embedding))
	for i, v := range or.Embedding {
		out[i] = float32(v)
	}
	return out, nil
}

func drainAndClose(body io.ReadCloser) {
	_, _ = io.Copy(io.Discard, io.LimitReader(body, 64<<10))
	_ = body.Close()
}
