// Package httpapi implements the server side of the ADR-0005 Transparency
// Log HTTP contract: POST /api/v1/log/entries.
package httpapi

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"

	"basicstack.de/proofedmesh/services/transparency-log/pkg/backend"
)

// Server is the HTTP handler. Mount it on /api/v1/log/entries via Handler().
// Authentication (Pocket-ID bearer tokens per ADR-0005) is intentionally
// NOT in this struct; it is wired by cmd/transparency-log/main.go through
// a middleware so that the dev/CI path can run without an IdP.
type Server struct {
	Backend  backend.Backend
	MaxBody  int64 // 0 → default 1 MiB
	LogError func(string, ...any)
}

// Handler returns an http.Handler that serves the ADR-0005 routes plus a
// liveness check at GET /healthz. Everything else is 404.
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.Handle("POST /api/v1/log/entries", http.HandlerFunc(s.handleSubmit))
	mux.Handle("GET /api/v1/log/entries/{hash}", http.HandlerFunc(s.handleGetEntry))
	mux.Handle("GET /healthz", http.HandlerFunc(s.handleHealth))
	return mux
}

func (s *Server) handleHealth(w http.ResponseWriter, _ *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write([]byte(`{"status":"ok"}`))
}

func (s *Server) handleGetEntry(w http.ResponseWriter, r *http.Request) {
	hash := r.PathValue("hash")
	if hash == "" {
		writeError(w, http.StatusBadRequest, "content_hash is required")
		return
	}
	entry, err := s.Backend.Get(r.Context(), hash)
	switch {
	case errors.Is(err, backend.ErrEntryNotFound):
		writeError(w, http.StatusNotFound, "entry not found")
		return
	case errors.Is(err, backend.ErrTrillianUnavailable):
		writeError(w, http.StatusServiceUnavailable, err.Error())
		return
	case err != nil:
		s.logErr("transparency-log get: %v", err)
		writeError(w, http.StatusInternalServerError, "internal error")
		return
	}
	writeJSON(w, http.StatusOK, entry)
}

type submitRequest struct {
	Envelope    backend.Envelope `json:"envelope"`
	ContentHash string           `json:"content_hash"`
}

type errorBody struct {
	Error string `json:"error"`
}

func (s *Server) handleSubmit(w http.ResponseWriter, r *http.Request) {
	if ct := r.Header.Get("Content-Type"); ct != "" && ct != "application/json" && !isJSONWithCharset(ct) {
		writeError(w, http.StatusBadRequest, "content-type must be application/json")
		return
	}
	max := s.MaxBody
	if max <= 0 {
		max = 1 << 20
	}
	raw, err := io.ReadAll(io.LimitReader(r.Body, max+1))
	if err != nil {
		writeError(w, http.StatusBadRequest, "read body: "+err.Error())
		return
	}
	if int64(len(raw)) > max {
		writeError(w, http.StatusRequestEntityTooLarge, fmt.Sprintf("body exceeds %d bytes", max))
		return
	}
	var req submitRequest
	dec := json.NewDecoder(bytesReader(raw))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "decode: "+err.Error())
		return
	}
	if req.ContentHash == "" {
		writeError(w, http.StatusBadRequest, "content_hash is required")
		return
	}

	receipt, fresh, err := s.Backend.Submit(r.Context(), req.Envelope, req.ContentHash)
	switch {
	case errors.Is(err, backend.ErrContentHashMismatch):
		writeError(w, http.StatusConflict, err.Error())
		return
	case errors.Is(err, backend.ErrTrillianUnavailable):
		writeError(w, http.StatusServiceUnavailable, err.Error())
		return
	case err != nil:
		s.logErr("transparency-log submit: %v", err)
		writeError(w, http.StatusInternalServerError, "internal error")
		return
	}
	status := http.StatusOK
	if fresh {
		status = http.StatusCreated
	}
	writeJSON(w, status, receipt)
}

func (s *Server) logErr(format string, args ...any) {
	if s.LogError != nil {
		s.LogError(format, args...)
	}
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, errorBody{Error: msg})
}

func isJSONWithCharset(ct string) bool {
	// Accept "application/json; charset=utf-8" and friends.
	const prefix = "application/json"
	if len(ct) < len(prefix) {
		return false
	}
	if ct[:len(prefix)] != prefix {
		return false
	}
	rest := ct[len(prefix):]
	return len(rest) == 0 || rest[0] == ';' || rest[0] == ' '
}

// bytesReader avoids pulling in bytes just for a reader over a []byte.
type sliceReader struct {
	b []byte
}

func (r *sliceReader) Read(p []byte) (int, error) {
	if len(r.b) == 0 {
		return 0, io.EOF
	}
	n := copy(p, r.b)
	r.b = r.b[n:]
	return n, nil
}

func bytesReader(b []byte) io.Reader { return &sliceReader{b: b} }