package control

import (
	"errors"
	"net/http"

	"github.com/tegwick/fluid-core/internal/contract"
	"github.com/tegwick/fluid-core/internal/science"
)

// ScienceAPI implements ArchitectureBlueprint.md sections 44.3 and 44.4: the
// hypothesis and experiment control surfaces.
//
// It is one type rather than two because the operations are entangled —
// starting an experiment moves its hypotheses, finalizing one moves them back —
// and splitting them would mean two handlers reaching into the same lifecycle.
type ScienceAPI struct {
	hypotheses  *science.HypothesisStore
	experiments *science.ExperimentController
}

// NewScienceAPI returns the hypothesis and experiment APIs.
func NewScienceAPI(h *science.HypothesisStore, e *science.ExperimentController) *ScienceAPI {
	return &ScienceAPI{hypotheses: h, experiments: e}
}

// ---------- hypotheses ----------

func (a *ScienceAPI) handleHypotheses(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		state := contract.FluidHypothesisState(r.URL.Query().Get("state"))
		if state != "" && !state.Valid() {
			writeError(w, http.StatusBadRequest, "unknown state filter")
			return
		}
		list, err := a.hypotheses.List(r.Context(), state)
		if err != nil {
			writeError(w, http.StatusInternalServerError, "could not list hypotheses")
			return
		}
		writeJSON(w, http.StatusOK, map[string]any{"hypotheses": list})

	case http.MethodPost:
		var req struct {
			Hypothesis contract.FluidHypothesis `json:"hypothesis"`
			Actor      contract.Actor           `json:"actor"`
		}
		if err := decodeBody(r, &req); err != nil {
			writeError(w, http.StatusBadRequest, "could not decode request", err.Error())
			return
		}
		if req.Actor.ID == "" {
			writeError(w, http.StatusBadRequest, "a hypothesis must name its author")
			return
		}

		h, err := a.hypotheses.Create(r.Context(), req.Hypothesis, req.Actor)
		if err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		writeJSON(w, http.StatusCreated, h)

	default:
		writeError(w, http.StatusMethodNotAllowed, "method not allowed")
	}
}

// TransitionRequest moves a hypothesis through its lifecycle.
type TransitionRequest struct {
	State  contract.FluidHypothesisState `json:"state,omitempty"`
	Reason string                        `json:"reason"`
	Actor  contract.Actor                `json:"actor"`

	// Outcome closes a hypothesis under evaluation.
	Outcome      *contract.FluidHypothesisOutcomeStatus `json:"outcome,omitempty"`
	Summary      string                                 `json:"summary,omitempty"`
	EvidenceRefs []contract.EvidenceRef                 `json:"evidence_refs,omitempty"`

	// AttachRevision and AttachExperiment link a hypothesis to its artifacts.
	AttachRevision   contract.RevisionID   `json:"attach_revision,omitempty"`
	AttachExperiment contract.ExperimentID `json:"attach_experiment,omitempty"`
}

func (a *ScienceAPI) handleHypothesisItem(w http.ResponseWriter, r *http.Request) {
	id := contract.HypothesisID(pathTail(r.URL.Path, "/control/v1/hypotheses"))
	if id == "" {
		writeError(w, http.StatusNotFound, "no hypothesis named")
		return
	}

	switch r.Method {
	case http.MethodGet:
		h, err := a.hypotheses.Get(r.Context(), id)
		if err != nil {
			writeError(w, statusForStoreError(err), "hypothesis not found")
			return
		}
		writeJSON(w, http.StatusOK, h)

	case http.MethodPatch:
		var req TransitionRequest
		if err := decodeBody(r, &req); err != nil {
			writeError(w, http.StatusBadRequest, "could not decode request", err.Error())
			return
		}
		if req.Actor.ID == "" {
			writeError(w, http.StatusBadRequest, "a lifecycle change must name its actor")
			return
		}

		if req.AttachRevision != "" {
			if err := a.hypotheses.AttachRevision(r.Context(), id, req.AttachRevision, req.Actor); err != nil {
				writeError(w, http.StatusBadRequest, err.Error())
				return
			}
		}
		if req.AttachExperiment != "" {
			if err := a.hypotheses.AttachExperiment(r.Context(), id, req.AttachExperiment, req.Actor); err != nil {
				writeError(w, http.StatusBadRequest, err.Error())
				return
			}
		}

		if req.Outcome != nil {
			h, err := a.hypotheses.RecordOutcome(r.Context(), id, *req.Outcome, req.Summary, req.EvidenceRefs, req.Actor)
			if err != nil {
				writeError(w, http.StatusBadRequest, err.Error())
				return
			}
			writeJSON(w, http.StatusOK, h)
			return
		}

		if req.State != "" {
			h, err := a.hypotheses.Transition(r.Context(), id, req.State, req.Actor, req.Reason)
			if err != nil {
				// An incomplete hypothesis or a forbidden move is the caller
				// being told what the lifecycle requires, not a server fault.
				status := http.StatusUnprocessableEntity
				if errors.Is(err, science.ErrNotFound) {
					status = http.StatusNotFound
				}
				writeError(w, status, err.Error())
				return
			}
			writeJSON(w, http.StatusOK, h)
			return
		}

		h, err := a.hypotheses.Get(r.Context(), id)
		if err != nil {
			writeError(w, statusForStoreError(err), "hypothesis not found")
			return
		}
		writeJSON(w, http.StatusOK, h)

	default:
		writeError(w, http.StatusMethodNotAllowed, "method not allowed")
	}
}

// CompeteRequest forms or resolves a competition group.
type CompeteRequest struct {
	GroupID string                  `json:"group_id"`
	Members []contract.HypothesisID `json:"members,omitempty"`
	Winner  contract.HypothesisID   `json:"winner,omitempty"`
	Reason  string                  `json:"reason,omitempty"`
	Actor   contract.Actor          `json:"actor"`
}

func (a *ScienceAPI) handleCompetition(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeError(w, http.StatusMethodNotAllowed, "method not allowed")
		return
	}

	var req CompeteRequest
	if err := decodeBody(r, &req); err != nil {
		writeError(w, http.StatusBadRequest, "could not decode request", err.Error())
		return
	}
	if req.Actor.ID == "" {
		writeError(w, http.StatusBadRequest, "a competition change must name its actor")
		return
	}

	if req.Winner != "" {
		group, err := a.hypotheses.Resolve(r.Context(), req.GroupID, req.Winner, req.Actor, req.Reason)
		if err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, group)
		return
	}

	group, err := a.hypotheses.Compete(r.Context(), req.GroupID, req.Members, req.Actor)
	if err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	writeJSON(w, http.StatusCreated, group)
}

// ---------- experiments ----------

func (a *ScienceAPI) handleExperiments(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		state := contract.FluidExperimentResultState(r.URL.Query().Get("state"))
		list, err := a.experiments.List(r.Context(), state)
		if err != nil {
			writeError(w, http.StatusInternalServerError, "could not list experiments")
			return
		}
		writeJSON(w, http.StatusOK, map[string]any{"experiments": list})

	case http.MethodPost:
		var req struct {
			Experiment contract.FluidExperiment `json:"experiment"`
			Actor      contract.Actor           `json:"actor"`
		}
		if err := decodeBody(r, &req); err != nil {
			writeError(w, http.StatusBadRequest, "could not decode request", err.Error())
			return
		}
		if req.Actor.ID == "" {
			writeError(w, http.StatusBadRequest, "an experiment must name its designer")
			return
		}

		e, err := a.experiments.Design(r.Context(), req.Experiment, req.Actor)
		if err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		writeJSON(w, http.StatusCreated, e)

	default:
		writeError(w, http.StatusMethodNotAllowed, "method not allowed")
	}
}

// ExperimentActionRequest drives an experiment's lifecycle.
//
// The routing policy that starting or stopping produces is returned to the
// caller rather than installed here. Blueprint section 17 keeps the controller
// out of the traffic path, and installing policy from this handler would put it
// straight back in.
type ExperimentActionRequest struct {
	Action string `json:"action"` // start, stop, finalize, amend

	Generation      int64               `json:"generation,omitempty"`
	DefaultRevision contract.RevisionID `json:"default_revision,omitempty"`

	Reason    string                 `json:"reason,omitempty"`
	Preferred contract.RevisionID    `json:"preferred_revision,omitempty"`
	Evidence  []contract.EvidenceRef `json:"evidence_refs,omitempty"`
	Change    string                 `json:"change,omitempty"`

	Actor contract.Actor `json:"actor"`
}

func (a *ScienceAPI) handleExperimentItem(w http.ResponseWriter, r *http.Request) {
	id := contract.ExperimentID(pathTail(r.URL.Path, "/control/v1/experiments"))
	if id == "" {
		writeError(w, http.StatusNotFound, "no experiment named")
		return
	}

	switch r.Method {
	case http.MethodGet:
		e, err := a.experiments.Get(r.Context(), id)
		if err != nil {
			writeError(w, statusForStoreError(err), "experiment not found")
			return
		}
		writeJSON(w, http.StatusOK, e)

	case http.MethodPost:
		var req ExperimentActionRequest
		if err := decodeBody(r, &req); err != nil {
			writeError(w, http.StatusBadRequest, "could not decode request", err.Error())
			return
		}
		if req.Actor.ID == "" {
			writeError(w, http.StatusBadRequest, "an experiment action must name its actor")
			return
		}
		a.act(w, r, id, req)

	default:
		writeError(w, http.StatusMethodNotAllowed, "method not allowed")
	}
}

func (a *ScienceAPI) act(w http.ResponseWriter, r *http.Request, id contract.ExperimentID, req ExperimentActionRequest) {
	switch req.Action {
	case "start":
		e, policy, err := a.experiments.Start(r.Context(), id, req.Generation, req.DefaultRevision, req.Actor)
		if err != nil {
			status := http.StatusBadRequest
			if errors.Is(err, science.ErrTooManyExperiments) {
				// The concurrency limit is a temporary condition, not a
				// malformed request.
				status = http.StatusConflict
			}
			writeError(w, status, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, map[string]any{
			"experiment":     e,
			"routing_policy": contract.RoutingPolicyDocument{RoutingPolicy: policy},
			"note":           "install this policy to expose the experiment; the controller does not route traffic itself",
		})

	case "stop":
		e, policy, err := a.experiments.Stop(r.Context(), id, req.Generation, req.DefaultRevision, req.Actor, req.Reason)
		if err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, map[string]any{
			"experiment":     e,
			"routing_policy": contract.RoutingPolicyDocument{RoutingPolicy: policy},
			"note":           "install this policy to return traffic to the default revision",
		})

	case "finalize":
		e, err := a.experiments.Finalize(r.Context(), id, req.Preferred, req.Actor, req.Reason, req.Evidence)
		if err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, e)

	case "amend":
		e, err := a.experiments.Amend(r.Context(), id, req.Change, req.Reason, req.Actor)
		if err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, e)

	default:
		writeError(w, http.StatusBadRequest,
			"unknown action; expected start, stop, finalize or amend")
	}
}